Many print applications and markets require watermarks on the hardcopy prints to encode information on job integrity or security. In certain markets and countries, security features are mandatory to prevent fraud. There are many different digital watermarking technologies and many of them are implemented by modifying or special processing of the documents. A well known current practice of “invisible” watermarking is the use of a yellow dots method, which is image rendering independent, to encode printer identification and time/date. However, some marking processes cannot use yellow dots because they suppress the development of black toner resulting in visible yellow dots in black regions of a print. Notably, the lack of a security encoding method has presented a challenge in markets that require security features, such as in government facilities.
It is very desirable to develop an alternative method, which is image rendering independent, to encode security data via invisible watermarks in image output devices such as laser printers.